For those who want to hack their Monotron, do it with Shematics directly from Korg:
http://www.korg-datastorage.jp/Manual/monotron_sch.pdf
That has been out for a couple of weeks or so. fcd72 already posted it up in the recent Akai/Monotron thread, here:
But it’s jolly decent of Korg to make it easier for us to void the warranty 
I’ve been quite busy with my Monotron already.
Thanks for the credit but it wasnt me . . my last Korg was the WaveStation 
Doh! My mistake, it was Phm78. Damn you pesky people with 3 letters and 2 numbers on the end for a name…
sorry for the double post 
…Certainly too much iron smokin…
We should find a way crystalizing the soldering smokes and then sell it… probably the next big hit and its not from middle-america!
would it be possible to modify a korg monotron so that it would work as a shruti filterboard?
This thing has no VCA and no VC-control on resonance. Would be easier to just redo the schematics with all the proper VC-controls set up. The “sound” of the MS-like filter is more due to the specific topology / transfer function than to the particular choice of parts. There’s no magic in there.